The present disclosure relates to a fixing device and an image forming apparatus therewith.
An image forming apparatus of an electrographic manner includes a fixing device which thermally fixes a toner image to a medium passing through a nip having been formed of a fixing member and a pressing member, each of which rotates. A surface of the fixing member is formed of an electrically insulating material, and may be charged at an opposite polarity to a polarity of the toner by way of friction with the medium passing through the nip. Then, there occurs an offset phenomenon that the toner on the medium adheres to the surface of the fixing member and subsequently the toner transfers to the medium passing through the nip later.
A technique for restraining the offset phenomenon is proposed. For example, there is proposed an image forming apparatus including: a transfer charger which charges a sheet at an opposite polarity to that of a toner in order to transfer a toner image on a photosensitive body; a separating charger which charges the sheet after transferred, at a same polarity as that of the toner; and a power source for offset prevention bias (charger for offset prevention) which charges a surface of a fixing roller of a fixing device at the same polarity as that of the toner. Each of the transfer charger, the separating charger, and the charger for offset prevention is a charger utilizing a corona discharge that has occurred in an electric field around an electrode. The charger for offset prevention varies an intensity of an electric field which is applied to the fixing roller, concurrently with a change of a static elimination charge amount exerted by the separating charger.